1. Field of the Invention
The present invention relates to N-alkylglycamino compounds, a process for producing them, and their use.
2. Description of the Background
Renewable agricultural products are important raw materials for the detergent and personal care sectors. In addition to vegetable oils and animal fats, starch and monosaccharides are gaining increased importance. The first polyglycosides and saccharide esters are already available on the market as environmentally harmless surfactants. Glycamines based on monosaccharides likewise represent good starting materials for surface active detergents and personal care applications. Thus, for example, tertiary and quaternary fatty alkylglycammonium salts are mentioned as cationic detergents (U.S. Pat. Nos. 2,060,850; 2,060,851). Corresponding ethoxylated compounds are suggested as low-foam rinses and detergents as well as skin and hair conditioners (French Patent 1,573,085; German Disclosure 22 00 040, Japanese Patents 59-212,419, 59-212 421). Also known are nonionic surfactants based on fatty acid N-alkylglycamides, that are particularly gentle on the skin and at the same time have a thickening effect on shampoo and shower bath formulations (U.S. Pat. No. 2,703,798; German Disclosure 37 11 776).
Amphoteric surfactants represent a class of substances that behave like anionic or cationic surfactants depending on the adjustment of the medium (acidic, neutral, or alkaline), i.e., they have electronegative and electropositive groups combined in the same molecule. They are gaining increased importance in the personal care sector since they have particularly good skin tolerability and low toxicity, and show good effect in weakly acidic media as mild surfactants.
In general, the amphoteric surfactants are N-substituted amino acids of the following type (Formula I): ##STR3## in which R.sub.1 stands for a longer fatty alkyl chain and R.sub.2, for example, stands for a shorter alkyl group. R.sub.3 can represent either a proton or an alkyl group. There is a clear distinction between the behavior of amino acids having tetrasubstituted nitrogen and those having trisubstituted nitrogen. That is, tetrasubstituted amino acids, which are also called betaines (Formula II), have a fixed positive charge independently of the pH of the medium. In the neutral and alkaline ranges the isoelectric, zwitterionic character is retained. In the acidic range the betaine behaves like a cationic surfactant. ##STR4##
The trisubstituted amino acids (Formula III), on the other hand, represent real ampholytes. ##STR5## In the neutral range they form internal salts. In acidic media they change into cations, and in the alkaline range into anions.
A drawback of the known N-trisubstituted amphoteric surfactants is that in the desired pH range, specifically weakly acidic to neutral, they show a minimum in solubility, foaming power, and wetting power when used in formulations which are employed in the personal care sector such as shampoos and shower materials [Tenside Detergents 23 (1986) 309]. A need therefore continues to exist for N-trisubstituted amphoteric surfactants which exhibit improved surfactant properties.